class User < ActiveRecord::Base
 has_many :statuses
end

class Status < ActiveRecord::Base
 belongs_to :user
end

在控制器中：

def index
    @statuses = []
    current_user.friends.map{ |friend| friend.statuses.each { |status| @statuses << status } }
    current_user.statuses.each { |status| @statuses << status }

    @statuses.sort! { |a,b| b.created_at <=> a.created_at }
end

current_user.friends返回一个对象数组

friend.statuses返回一个对象的数组状态

错误：

comparison of Status with Status Failed
app/controllers/welcome_controller.rb:10:in `sort!'
app/controllers/welcome_controller.rb:10:in `index'